Method for bulk polymerization

ABSTRACT

A method for polymerizing conjugated diene monomer into polydienes, the method comprising: polymerizing conjugated diene monomer within a liquid-phase polymerization mixture that includes conjugated diene monomer, a lanthanide-based catalyst system, dicyclopentadiene or substituted dicyclopentadiene, and optionally organic solvent, with the proviso that the organic solvent, if present, is less than about 20% by weight based on the total weight of the polymerization mixture.

FIELD OF THE INVENTION

One or more embodiments of the invention relate to a method for the bulkpolymerization of conjugated diene monomer in the presence ofdicyclopentadiene or substituted dicyclopentadiene.

BACKGROUND OF THE INVENTION

Polydienes are most often produced by solution polymerization, whereinconjugated diene monomer is polymerized in an inert solvent or diluent.The solvent serves to solubilize the reactants and product, to act as acarrier for the reactants and product, to aid in the transfer of theheat of polymerization, and to help in moderating the polymerizationrate. The solvent also allows easier stirring and transferring of thepolymerization mixture (also called cement), since the viscosity of thecement is decreased by the presence of the solvent.

Nevertheless, the presence of the solvent presents a number ofdifficulties. The solvent must be separated from the polymer and thenrecycled for reuse or otherwise disposed of as waste. The cost ofrecovering and recycling the solvent adds greatly to the cost of thepolymer being produced, and there is always the risk that the recycledsolvent after purification may still retain some impurities that willpoison the polymerization catalyst. In addition, some solvents such asaromatic hydrocarbons can raise environmental concerns. Further, thepurity of the polymer product may be affected if there are difficultiesin removing the solvent.

Polydienes may also be produced by bulk polymerization (also called masspolymerization), wherein the polymerization mixture is typicallysolventless; i.e., the monomer is polymerized in the absence orsubstantial absence of any solvent, and in effect, the monomer itselfacts as a diluent. Since bulk polymerization involves mainly monomer andcatalyst, there is reduced potential for contamination and the productseparation may be simplified. Economic advantages including lowercapital cost for new plant capacity, lower energy cost to operate, andfewer people to operate may be realized. The solventless feature mayalso provide environmental advantages with reduced emissions andwastewater pollution.

Nonetheless, bulk polymerization may require careful temperaturecontrol, and there may be a need for strong and elaborate stirringequipment since the viscosity of the polymerization mixture may becomevery high. In the absence of added diluent, the cement viscosity andexotherm effects may make temperature control very difficult. Also,cis-1,4-polybutadiene is insoluble in 1,3-butadiene monomer at elevatedtemperatures. Consequently, local hot spots may occur, resulting indegradation, gelation, and/or discoloration of the polymer product. Inthe extreme case, disastrous “runaway” reactions may occur.

Olefins, which are distinct from conjugated dienes, have commonly beenpolymerized by gas-phase polymerization or slurry-phase polymerizationtechniques that employ solid-supported catalysts. These gas-phase orslurry polymerization processes have been plagued by reactor fouling orsheeting, which has caused operability problems. For example, fouling ofgas-phase polymerization reactors during the production of polyethyleneor polypropylene is a well known problem. It is believed that thisfouling is caused by an uncontrolled reaction caused by catalystembedded within polymer stuck to reactor or pipe surfaces.

The prior art has addressed the problems of fouling or sheeting withingas-phase or slurry-phase reactors employed for olefin polymerization byemploying several approaches. For example, U.S. Pat. No. 6,632,769discloses the use of additives that change phase when heated and therebyrelease a catalyst poison. U.S. Pat. No. 6,346,584 describes the use ofa binary system that reacts above a desired threshold temperature togenerate a catalyst poison. U.S. Pat. No. 6,713,573 discloses the use ofadditive systems that undergo thermal decomposition at temperaturesabove a desired threshold to generate a catalyst poison. U.S. Pat. No.4,942,147 discloses a transition metal catalyst system containing anautoacceleration inhibitor.

Since the advantages associated with bulk polymerization systems arevery attractive, there is a need to improve bulk polymerization systems.Further, a method is needed to prevent runaway reactions in liquid-phasebulk polymerizations.

Arriving at a solution to prevent runaway reactions duringlanthanide-catalyzed conjugated diene polymerization, however, is nottrivial. Unlike gas-phase or slurry-phase olefin polymerization, thebulk polymerization of conjugated dienes occurs in the liquid phase.And, the catalyst system is dissolved in the monomer/polydiene mixture.Moreover, lanthanide-based catalyst systems are notoriously susceptibleto impurities. That is, various impurities can have a deleterious impacton these catalyst systems and the polymerizations in which they areused.

SUMMARY OF THE INVENTION

In one or more embodiments, the present invention provides a method forpolymerizing conjugated diene monomer into polydienes, the methodcomprising: polymerizing conjugated diene monomer within a liquid-phasepolymerization mixture that includes conjugated diene monomer, alanthanide-based catalyst system, dicyclopentadiene or substituteddicyclopentadiene, and optionally organic solvent, with the proviso thatthe organic solvent, if present, is less than about 20% by weight basedon the total weight of the polymerization mixture.

In one or more embodiments, the present invention also provides a methodfor preparing a polydiene, the method comprising the steps of: (i)introducing conjugated diene monomer, a lanthanide-based catalystsystem, dicyclopentadiene or substituted dicyclopentadiene, andoptionally organic solvent to a reactor to form a liquid-phasepolymerization mixture including less than 20% by weight of organicsolvent based on the total weight of the polymerization mixture; and(ii) allowing the monomer to polymerize in the presence of thelanthanide-based catalyst system and the dicyclopentadiene orsubstituted dicyclopentadiene within the liquid-phase polymerizationmixture to form a polydiene.

Other embodiments of the present invention provide a compositioncomprising: (i) a lanthanide-based catalyst system; (ii) conjugateddiene monomer; (iii) polydiene; and (iv) dicyclopentadiene orsubstituted dicyclopentadiene, with the proviso that the compositionincludes less than about 20% by weight of organic solvent based on thetotal weight of the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a temperature and pressure profile of the polymerizationdescribed in Example 3.

FIG. 2 is a temperature and pressure profile of the polymerizationdescribed in Example 4.

FIG. 3 is a temperature and pressure profile of the polymerizationdescribed in Example 6.

FIG. 4 is a temperature and pressure profile of the polymerizationdescribed in Example 7.

FIG. 5 is a temperature and pressure profile of the polymerizationdescribed in Example 8.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

One or more embodiments of the present invention provide a method forthe bulk polymerization of conjugated diene monomer in the presence ofdicyclopentadiene or substituted dicyclopentadiene. In one or moreembodiments, a lanthanide-based catalyst system is employed to effectthe polymerization. It has unexpectedly been discovered thatdicyclopentadiene or substituted dicyclopentadiene can be presentwithout a deleterious impact on the bulk polymerization of theconjugated diene monomer while gaining the benefit of a compound thatwill thermally decompose and deactivate the catalyst. Advantageously,this decomposition takes place at temperatures above where thepolymerization takes place but below temperatures where thepolymerization can no longer be controlled.

The polymerization of conjugated diene according to this invention takesplace within a bulk or high-solids polymerization mixture. Within thismixture, liquid-phase monomer is converted to polymer, which may or maynot be soluble in the monomer. As those skilled in the art appreciate,there may be an equilibrium between monomer in the gas phase and monomerwithin the liquid phase in the reactor. Those skilled in the art alsounderstand that the equilibrium may be affected by various conditions.Nonetheless, polymerization of monomer according to the presentinvention occurs in the liquid phase.

In one or more embodiments, the polymerization process of the presentinvention is conducted within a polymerization mixture that includesless than about 20%, in other embodiments less than about 10%, in otherembodiments less than about 5%, and in other embodiments less than about2% by weight organic solvent based on the total weight of the monomer,polymer, and solvent within the mixture. In one embodiment, the processis carried out in the substantial absence of an organic solvent ordiluent, which refers to the absence of that amount of solvent thatwould otherwise have an appreciable impact on the polymerizationprocess. Stated another way, those skilled in the art will appreciatethe benefits of bulk polymerization processes (i.e., processes wheremonomer acts as the solvent), and therefore the process of thisinvention may be conducted in the presence of less organic solvent thanwill deleteriously impact the benefits sought by conducting the processin bulk. In another embodiment, the process may be carried out in theabsence of an organic solvent or diluent other than those organicsolvents or diluents that are inherent to the raw materials employed. Inyet another embodiment, the polymerization system is devoid of organicsolvent.

A variety of organic solvents may be employed in practicing the presentinvention. The term organic solvent or diluent is used hereinconventionally; that is, it refers to organic compounds that will notpolymerize or enter into the structure of the polymer to be produced.Typically, these organic solvents are non-reactive or inert to thecatalyst composition. Exemplary organic solvents include aromatichydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons.Non-limiting examples of aromatic hydrocarbons include benzene, toluene,xylenes, ethylbenzene, diethylbenzene, and mesitylene. Non-limitingexamples of aliphatic hydrocarbons include n-pentane, n-hexane,n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes,isopentanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene,and petroleum spirits. And, non-limiting examples of cycloaliphatichydrocarbons include cyclopentane, cyclohexane, methylcyclopentane, andmethylcyclohexane. Commercial mixtures of the above hydrocarbons mayalso be used.

Other examples of organic solvents include high-boiling hydrocarbons ofhigh molecular weights, such as paraffinic oil, aromatic oil, or otherhydrocarbon oils that are commonly used to oil-extend polymers. Sincethese hydrocarbons are non-volatile, they typically do not requireseparation and remain with the polymer. The performance characteristicsof the polymer are generally not affected appreciably when the contentof high molecular weight hydrocarbons is less than about 5% by weight ofthe polymer.

Various conjugated diene monomer or mixtures thereof can be employed.Examples of conjugated diene monomer include 1,3-butadiene, isoprene,1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2-methyl-1,3-penta-diene,3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 2,4-hexadiene, andmixtures thereof.

In certain embodiments, it may be beneficial to control the humidity(i.e., water content) of the monomer. For example, where certainlanthanide-based catalyst systems are employed, it may be beneficial todry the monomer. In one embodiment, the level of water within themonomer is reduced below about 20 ppm, in other embodiments below about10 ppm, in other embodiments below about 5 ppm, and in other embodimentsbelow about 3 ppm.

In one or more embodiments, the catalyst system employed in practicingthe process of this invention is a lanthanide-based catalyst system. Inone or more embodiments, the lanthanide-based catalyst system is formedby combining (a) a lanthanide compound, (b) an alkylating agent, and (c)a halogen-containing compound. Other reagents such as otherorganometallic compounds or Lewis bases may also optionally be included.Lanthanide-based catalyst systems are well known in the art as describedin U.S. Pat. Nos. 3,297,667, 3,541,063, 3,794,604, 4,461,883, 4,444,903,4,525,594, 4,699,960, 5,017,539, 5,428,119, 5,064,910, and 5,844,050,which are incorporated herein by reference, as well as co-pending U.S.Ser. No. 10/468,515, which is likewise incorporated herein by reference.

Various lanthanide compounds or mixtures thereof may be employed asingredient (a) of the lanthanide-based catalyst system. In one or moreembodiments, these compounds are soluble in hydrocarbon solvents such asaromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatichydrocarbons. Hydrocarbon-insoluble lanthanide compounds, however, maybe suspended in the polymerization mixture to form the catalyticallyactive species and are also useful.

Lanthanide compounds include at least one atom of lanthanum, neodymium,cerium, praseodymium, promethium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, anddidymium. In particular embodiments, these compounds include neodymium,lanthanum, samarium, or didymium. Didymium is a commercial mixture ofrare-earth elements obtained from monazite sand.

The lanthanide atom in the lanthanide compounds may be in variousoxidation states including but not limited to the 0, +2, +3, and +4oxidation states. Trivalent lanthanide compounds, where the lanthanideatom is in the +3 oxidation state, are particularly useful in one ormore embodiments. Suitable lanthanide compounds include, but are notlimited to, lanthanide carboxylates, lanthanide organophosphates,lanthanide organophosphonates, lanthanide organophosphinates, lanthanidecarbamates, lanthanide dithiocarbamates, lanthanide xanthates,lanthanide β-diketonates, lanthanide alkoxides or aryloxides, lanthanidehalides, lanthanide pseudo-halides, lanthanide oxyhalides, andorganolanthanide compounds.

Various alkylating agents, or mixtures thereof, may be used as component(b) of the lanthanide-based catalyst system. Alkylating agents, whichmay also be referred to as hydrocarbylating agents, are organometalliccompounds that may transfer hydrocarbyl groups to another metal.Typically, these agents are organometallic compounds of electropositivemetals such as Groups 1, 2, and 3 metals (Groups IA, IIA, and IIIAmetals). Preferred alkylating agents include organoaluminum andorganomagnesium compounds. Where the alkylating agent includes a labilehalogen atom, the alkylating agent may also serve as thehalogen-containing compound. In one or more embodiments, mixedalkylating systems may be used such as those disclosed in U.S. Pat. No.7,094,849, which is incorporated herein by reference.

The term “organoaluminum compound” refers to any aluminum compoundcontaining at least one aluminum-carbon bond. Organoaluminum compoundsthat are soluble in a hydrocarbon solvent are preferred.

One class of organoaluminum compounds that may be utilized isrepresented by the general formula AlR_(n)X_(3-n), where each R, whichmay be the same or different, is a mono-valent organic group that isattached to the aluminum atom via a carbon atom, where each X, which maybe the same or different, is a hydrogen atom, a halogen atom, acarboxylate group, an alkoxide group, or an aryloxide group, and where nis an integer of 1 to 3. Each R may be a hydrocarbyl group such as, butnot limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl,cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, aralkyl,alkaryl, allyl, and alkynyl groups, with each group preferablycontaining from 1 carbon atom, or the appropriate minimum number ofcarbon atoms to form the group, up to about 20 carbon atoms. Thesehydrocarbyl groups may contain heteroatoms such as, but not limited to,nitrogen, oxygen, boron, silicon, sulfur, and phosphorus atoms.

Another class of suitable organoaluminum compounds is aluminoxanes.Aluminoxanes comprise oligomeric linear aluminoxanes that may berepresented by the general formula:

and oligomeric cyclic aluminoxanes that may be represented by thegeneral formula:

where x is an integer of 1 to about 100, preferably about 10 to about50; y is an integer of 2 to about 100, preferably about 3 to about 20;and where each R¹, which may be the same or different, is a mono-valentorganic group that is attached to the aluminum atom via a carbon atom.Each R¹ may be a hydrocarbyl group such as, but not limited to, alkyl,cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substitutedcycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, andalkynyl groups, with each group preferably containing from 1 carbonatom, or the appropriate minimum number of carbon atoms to form thegroup, up to about 20 carbon atoms. These hydrocarbyl groups may containheteroatoms such as, but not limited to, nitrogen, oxygen, boron,silicon, sulfur, and phosphorus atoms. It should be noted that thenumber of moles of the aluminoxane as used in this application refers tothe number of moles of the aluminum atoms rather than the number ofmoles of the oligomeric aluminoxane molecules. This convention iscommonly employed in the art of catalysis utilizing aluminoxanes.

Aluminoxanes may be prepared by reacting trihydrocarbylaluminumcompounds with water. This reaction may be performed according to knownmethods, such as (1) a method in which the trihydrocarbylaluminumcompound is dissolved in an organic solvent and then contacted withwater, (2) a method in which the trihydrocarbylaluminum compound isreacted with water of crystallization contained in, for example, metalsalts, or water adsorbed in inorganic or organic compounds, and (3) amethod in which the trihydrocarbylaluminum compound is reacted withwater in the presence of the monomer or monomer solution that is to bepolymerized.

The term organomagnesium compound refers to any magnesium compound thatcontains at least one magnesium-carbon bond. Organomagnesium compoundsthat are soluble in a hydrocarbon solvent are preferred. One class oforganomagnesium compounds that may be utilized is represented by thegeneral formula MgR₂, where each R, which may be the same or different,is a mono-valent organic group, with the proviso that the group isattached to the magnesium atom via a carbon atom. Each R may be ahydrocarbyl group such as, but not limited to, alkyl, cycloalkyl,substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl,aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups,with each group preferably containing from 1 carbon atom, or theappropriate minimum number of carbon atoms to form the group, up toabout 20 carbon atoms. These hydrocarbyl groups may contain heteroatomssuch as, but not limited to, nitrogen, oxygen, silicon, sulfur, andphosphorus atom.

Another class of organomagnesium compounds that may be utilized asingredient (b) is represented by the general formula RMgX, where R is amono-valent organic group, with the proviso that the group is attachedto the magnesium atom via a carbon atom, and X is a hydrogen atom, ahalogen atom, a carboxylate group, an alkoxide group, or an aryloxidegroup. Preferably, R is a hydrocarbyl group such as, but not limited to,alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl,substituted cycloalkenyl, aryl, allyl, substituted aryl, aralkyl,alkaryl, and alkynyl groups, with each group preferably containing from1 carbon atom, or the appropriate minimum number of carbon atoms to formthe group, up to about 20 carbon atoms. These hydrocarbyl groups maycontain heteroatoms such as, but not limited to, nitrogen, oxygen,boron, silicon, sulfur, and phosphorus atoms. Preferably, X is acarboxylate group, an alkoxide group, or an aryloxide group, with eachgroup preferably containing 1 to 20 carbon atoms.

Various compounds, or mixtures thereof, that contain one or more labilehalogen atoms may be employed as ingredient (c) of the lanthanide-basedcatalyst system. These compounds may simply be referred to ashalogen-containing compounds. Examples of halogen atoms include, but arenot limited to, fluorine, chlorine, bromine, and iodine. A combinationof two or more halogen atoms may also be utilized. Halogen-containingcompounds that are soluble in a hydrocarbon solvent are preferred.Hydrocarbon-insoluble halogen-containing compounds, however, may besuspended in the oligomerization medium to form the catalytically activespecies, and are therefore useful.

Useful types of halogen-containing compounds include, but are notlimited to, elemental halogens, mixed halogens, hydrogen halides,organic halides, inorganic halides, metallic halides, organometallichalides, and mixtures thereof.

The lanthanide-based catalyst system has very high catalytic activityfor polymerizing conjugated dienes into stereoregular polydienes over awide range of catalyst concentrations and catalyst ingredient ratios. Itis believed that the catalyst ingredients (a), (b), and (c) may interactto form an active catalyst species. Accordingly, the optimumconcentration for any one catalyst ingredient is dependent upon theconcentrations of the other catalyst ingredients. In one embodiment, themolar ratio of the alkylating agent to the lanthanide compound(alkylating agent/Ln) may be varied from about 1:1 to about 200:1, inother embodiments from about 2:1 to about 100:1, and in otherembodiments from about 5:1 to about 50:1. The molar ratio of thehalogen-containing compound to the lanthanide compound (halogen atom/Ln)may be varied from about 0.5:1 to about 20:1, in other embodiments fromabout 1:1 to about 10:1, and in other embodiments from about 2:1 toabout 6:1. The term molar ratio, as used herein, refers to theequivalent ratio of relevant components of the ingredients, e.g.,equivalents of halogen atoms on the halogen-containing compound tolanthanide atoms on the lanthanide compound.

The lanthanide-based catalyst system may be formed by combining ormixing the catalyst ingredients (a), (b), and (c). Although an activecatalyst species is believed to result from this combination, the degreeof interaction or reaction between the various ingredients or componentsis not known with any great degree of certainty. Therefore, the term“catalyst system” or “catalyst composition” has been employed toencompass a simple mixture of the ingredients, a complex of the variousingredients that is caused by physical or chemical forces of attraction,a chemical reaction product of the ingredients, or a combination of theforegoing.

The production of polymer by using the lanthanide-based catalyst systemgenerally employs a catalytically effective amount of the foregoingcatalyst composition. The total catalyst concentration to be employed inthe polymerization mass depends on the interplay of various factors suchas the purity of the ingredients, the polymerization temperature, thepolymerization rate and conversion desired, the molecular weightdesired, and many other factors. Accordingly, a specific total catalystconcentration may not be definitively set forth except to say thatcatalytically effective amounts of the respective catalyst ingredientsshould be used. In one or more embodiments, the amount of the lanthanidecompound used may be varied from about 0.001 to about 2 mmol, in otherembodiments from about 0.01 to about 1 mmol, and in other embodimentsfrom about 0.05 to about 0.5 mmol per 100 g of conjugated diene monomer.

Dicyclopentadiene, substituted dicyclopentadiene, or mixtures thereofcan be employed in the present invention. As is known in the art,dicyclopentadiene is a dimer of cyclopentadiene. Substituteddicyclopentadiene is a dimer of substituted cyclopentadiene wherein oneor more of the hydrogen atoms of cyclopentadiene are replaced with asubstituent such as a hydrocarbyl group. Substituted dicyclopentadienecan be a homo-dimer that is formed by the dimerization of two moleculesof the same substituted cyclopentadiene. Substituted dicyclopentadienecan also be a hetero-dimer that is formed by the cross-dimerization ofone molecule of a substituted cyclopentadiene with one molecule ofanother different substituted cyclopentadiene. Substituteddicyclopentadiene can have various isomers depending on the positions ofthe substituents.

In one or more embodiments, dicyclopentadiene or substituteddicyclopentadiene may be represented by the following formula:

where each R is individually selected from the group consisting of ahydrogen atom and a hydrocarbyl group. In one or more embodiments, thehydrocarbyl groups, which may include substituted hydrocarbyl groups,can include, but are not limited to, alkyl, cycloalkyl, substitutedcycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl,allyl, substituted aryl, aralkyl, alkaryl, or alkynyl groups. In one ormore embodiments, these groups may include from one, or the appropriateminimum number of carbon atoms to form the group, to 20 carbon atoms.

Specific examples of substituted dicyclopentadiene compounds includedimethyldicyclopentadiene, diethyldicyclopentadiene,dicyclohexyldicyclopentadiene, and diphenyldicyclopentadiene. Each ofthese substituted dicyclopentadiene compounds can have various isomersdepending on the positions of the hydrocarbyl substituents. Thoseskilled in the art appreciate that dicyclopentadiene or substituteddicyclopentadiene may also be referred to as cyclopentadiene dimer orsubstituted cyclopentadiene dimer. For example, dicyclopentadiene may bereferred to as cyclopentadiene dimer, and dimethyldicyclopentadiene maybe referred to as methylcyclopentadiene dimer. For ease of description,dicyclopentadiene and substituted dicyclopentadiene may be collectivelyreferred to as Cp dimer.

In one or more embodiments, the amount of Cp dimer employed may bedescribed with respect to the molar ratio of Cp dimer to the lanthanidecompound (Cp dimer/Ln). In one or more embodiments, the molar ratio ofCp dimer to the lanthanide compound is at least 0.1:1, in otherembodiments at least 0.5:1, in other embodiments at least 1.0:1, and inother embodiments at least 1.5:1. In these or other embodiments, themolar ratio of Cp dimer to the lanthanide compound is less than 5:1, inother embodiments less than 4:1, in other embodiments less than 3:1, andin other embodiments less than 2.5:1.

In one or more embodiments, the bulk polymerization process is initiatedby providing in a reaction vessel a polymerizable composition thatincludes monomer, the catalyst system, and Cp dimer. Because thepolymerization may be carried out as a batch process, a continuousprocess, or a semi-continuous process, the manner in which the monomer,catalyst system and Cp dimer are charged may vary. In one or moreembodiments, the polymerization process is conducted under anaerobicconditions. Bulk polymerization of conjugated dienes is furtherdescribed in U.S. Pat. No. 7,094,849 and U.S. Published App. No.2005/0197474 A1, both of which are incorporated herein by reference.

In one or more embodiments, especially where the conversion is to beless than about 60%, the bulk polymerization may be conducted in aconventional stirred-tank reactor. For higher conversions, an elongatedreactor in which the cement under polymerization is driven to move bypiston, or extruders in which the cement is pushed along by aself-cleaning single-screw or double-screw agitator may be employed.

In one or more embodiments, the catalyst ingredients may be charged tothe vessel or reactor employed for polymerization by using a variety oftechniques and orders of addition. In one embodiment, a small quantityof an organic solvent may be employed as a carrier to either dissolve orsuspend the catalyst ingredients in order to facilitate the delivery ofthe catalyst ingredients to the polymerization system. In yet anotherembodiment, conjugated diene monomer may be used as the catalystcarrier. In one embodiment, the lanthanide-based system may bepre-formed and aged prior to use.

In one or more embodiments, Cp dimer may be pre-mixed with one or morecomponents of the catalyst system. In other embodiments, the Cp dimermay be pre-mixed with the monomer prior to contacting the monomer withall of the catalyst ingredients. In other embodiments, the lanthanidecompound and the Cp dimer may be introduced to the monomer to bepolymerized prior to introducing the remaining catalyst ingredients tothe monomer. In one or more embodiments, the Cp dimer may be aged withone or more of the catalyst ingredients. In other embodiments, the Cpdimer may be introduced into the reactor via a separate feed line.

In one or more embodiments, the temperature and pressure within thereactor is controlled to maintain the bulk of the monomer in the liquidphase. In one or more embodiments, the polymerization temperature may becontrolled below about 80° C., in other embodiments below about 55° C.,and in other embodiments below about 45° C., with one or moreembodiments being from about 15° C. to about 33° C., and otherembodiments from about 24° C. to about 32° C.

In one or more embodiments, the temperature of the polymerizationmixture may be controlled by externally cooling the vessel in which thepolymerization takes place, internally cooling the reaction by removalof monomer vapor, or by using a combination of the two methods. In oneembodiment, monomer vapor may be removed from the vessel and condensedfor future polymerization within the process. For example, anauto-refrigeration loop may be employed whereby monomer vapor may beremoved from the vessel, condensed, and re-circulated back into thevessel. In other embodiments, the vessel may be equipped with anevaporation column that may be controlled by water flow and/or watertemperature. Alternatively, the vapor may be removed, condensed, and themonomer condensate may be fed to a storage tank.

In one or more embodiments, an appropriate head space may be maintainedwithin the vessel to achieve a desired cooling effect from thevaporization of monomer. This head space, which includes that volume ofthe vessel that is not filled with the polymerization mixture but whichmay contain monomer vapor, may be about 35% to about 65%, and in otherembodiments from about 45% to about 55% by volume of the vessel.

Advantageously, Cp dimer is substantially inert to the lanthanide-basedcatalyst system at useful operating temperatures. But, atinappropriately high temperatures (i.e., temperatures at which a runawayreaction may occur), Cp dimer undergoes thermal decomposition to formcyclopentadiene or substituted cyclopentadiene, which inactivates thelanthanide-based catalyst and thereby terminates the polymerization.Thus, runaway reactions may be avoided. In one or more embodiments, theCp dimer decomposes to form cyclopentadiene or substitutedcyclopentadiene at a temperature of 100° C. or greater. In one or moreembodiments, the polymerization is terminated if the polymerizationtemperature reaches 100° C. or greater.

When the reaction temperature is maintained at less than 100° C., thebulk polymerization according to this invention may be carried out toany desired conversions before the polymerization is terminated. Incertain embodiments, however, high cement viscosity may result at highconversions. This may result in the separation of polymer as a solidphase from the monomer due to the limited solubility of, for example,cis-1,4-polybutadiene in 1,3-butadiene monomer.

In one or more embodiments, monomer is allowed to polymerize to amaximum monomer conversion of up to about 60%, in other embodiments upto about 40%, in other embodiments up to about 20%, and in yet otherembodiments up to about 10%, based upon the total weight of monomeradded to the polymerization mixture. In one embodiment, the monomerconversion is in the range of from about 5% to about 60%, in anotherembodiment, from about 10% to about 40%, and in yet another embodiment,from about 15% to 30%, In these or other embodiments, the polymerizationmixture may be characterized as a single-phase homogeneous mixture.

The polymerization reaction may be terminated by using techniques knownin the art. For example, useful techniques include the addition of aprotonating or quenching agent. These compounds are believed to react orinteract with living or pseudo-living polymer chains and prevent furtherchain growth or polymerization.

For example, reactive or reacting polymers may be quenched or protonatedby reacting them with a proton source. Compounds or agents that may beemployed to provide a proton source include water, alcohols (e.g.,isopropyl alcohol), butylated hydroxyl toluene (BHT), organic acids(e.g., carboxylic acids), and inorganic acids. In one or moreembodiments, an antioxidant such as 2,6-di-tert-butyl-4-methylphenol maybe added along with, before, or after the addition of the terminator.The amount of the antioxidant employed is typically in the range ofabout 0.2% to about 1% by weight of the polymer product. In one or moreembodiments, the terminator and the antioxidant may be added as neatmaterials or, if necessary, they may be dissolved in a hydrocarbonsolvent or conjugated diene monomer prior to being added to thepolymerization mixture.

Optionally, the living or pseudo-living polymers may be reacted with afunctionalizing agent or coupling agent prior to termination. Exemplaryfunctionalizing or coupling agents include, but are not limited to,metal halides, metalloid halides, alkoxysilanes, imine-containingcompounds, esters, ester-carboxylate metal complexes, alkyl estercarboxylate metal complexes, aldehydes or ketones, amides, isocyanates,isothiocyanates, imines, and epoxides. These types of coupling andfunctionalizing agents are described in, among other places, U.S.application Ser. Nos. 10/296,082 and 10/296,084; U.S. Pat. Nos.4,906,706, 4,990,573, 5,064,910, 5,567,784, and 5,844,050; JapanesePatent Application Nos. 05-051406A, 05-059103A, 10-306113A, and11-035633A, which are incorporated herein by reference. The polymer,which may be living or pseudo-living, may be contacted with a couplingor functionalizing agent prior to contacting the polymerization mixturewith the terminator or an antioxidant.

In one or more embodiments, the amount of coupling or functionalizingagent employed may vary from about 0.01 to about 100 moles, in otherembodiments from about 0.1 to about 50 moles, and in other embodimentsfrom about 0.2 to about 25 moles per mole of the living or pseudo-livingpolymer.

When the polymerization has been stopped, the polymer product may berecovered from the polymerization mixture by using any conventionalprocedures of desolventization and drying that are known in the art.Monomer and solvent may be removed by employing a variety of techniques,or a combination thereof, as is known in the art. For example, thetemperature of the polymerization mixture may be increased or maintainedat a temperature sufficient to volatilize the monomer. Also, thepressure within the vessel may be decreased, which may likewise assistin the volatilization of monomer. Still further, the polymerizationmixture may be agitated, which may further assist in the removal ofmonomer from the polymerization mixture. In one embodiment, acombination of heat, decreased pressure, and agitation may be employed.In one embodiment, a devolatilizer may be employed. Devolatilizers mayinclude a devolatilizing extruder, which typically includes a screwapparatus that may be heated by an external heating jacket. Theseextruders are known in the art such as single and twin screw extruders.The polymer product may then be baled, and in certain embodiments dicedor pelletized prior to baling.

In one or more embodiments, the bulk polymerization process may becharacterized as a multi-step process, and includes a first stagewherein partial polymerization of available monomer is achieved in thebulk phase followed by a second stage where at least a portion ofunreacted monomer is removed and the degree of polymerization iscontrolled. A multi-step bulk polymerization process is described inU.S. Published Patent Application No. 2005/0197474 A1, which isincorporated herein by reference.

In one or more embodiments, the first stage of the process includes acontinuous polymerization process whereby catalyst, monomer, and Cpdimer are continuously fed to a vessel and a portion of thepolymerization mixture is continuously removed from the vessel. Inasmuchas the degree of polymerization or monomer conversion is controlled inthe first stage, the polymerization mixture removed from the vessel mayinclude monomer, polymer, residual catalyst, and Cp dimer.

Once the desired monomer conversion is achieved in the first stage ofthe process, the polymerization mixture may be removed from the firstvessel employed in the first stage and transferred to a second stage,which takes place in a second vessel. Within this second stage, thepolymerization reaction may be terminated. Alternatively, thepolymerization reaction may be terminated between the first and secondstages. In one or more embodiments, the second stage of the processincludes the separation of solvent and unreacted monomer from thepolymer product. In those embodiments where the polymer product from thesecond stage contains more than a desired amount of solvent or unreactedmonomer, additional treatment of the polymer product may be carried out.

In one or more embodiments, the process of this invention may allow forthe production of polymers having targeted properties. In certainembodiments, the process may advantageously be employed to synthesizepolybutadiene having particular characteristics that allow thepolybutadiene to be employed for specialized uses.

In one or more embodiments, the process of this invention may producepolybutadiene having a molecular weight distribution of less than 4, inother embodiments less than 3.5, in other embodiments less than 3, andin other embodiments less than 2.5.

In one or more embodiments, the process of this invention mayadvantageously be employed to produce polybutadiene having a cis contentin excess of about 97, in other embodiments in excess of about 98, andin other embodiments in excess of about 99.

In one or more embodiments, the polymers may advantageously besynthesized to have a number average molecular weight of about 40,000 toabout 250,000, in other embodiments, about 60,000 to about 200,000, andin yet other embodiments, 80,000 to about 150,000. In one or moreembodiments, the polymers may be characterized by a Mooney Viscosity(ML₁₊₄) of about 10 to about 80, in other embodiments, about 20 to about70, and in yet other embodiments, about 30 to about 50.

The characteristics of the polymers produced according to this inventionmake them advantageous for a number of uses. For example, thecis-1,4-polybutadiene exhibits excellent viscoelastic properties and isparticularly useful in the manufacture of various tire componentsincluding, but not limited to, tire treads, sidewalls, subtreads, andbead fillers. The cis-1,4-polybutadiene may be used as all or part ofthe elastomeric component of a tire stock. When thecis-1,4-polybutadiene is used in conjunction with other rubbers to formthe elastomeric component of a tire stock, these other rubbers may benatural rubber, synthetic rubbers, and mixtures thereof. Examples ofsynthetic rubber include polyisoprene, poly(styrene-co-butadiene),polybutadiene with low cis-1,4 linkage content,poly(styrene-co-butadiene-co-isoprene), and mixtures thereof. Thecis-1,4-polybutadiene may also be used in the manufacture of hoses,belts, shoe soles, window seals, other seals, vibration damping rubber,and other industrial products.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested. The examples shouldnot, however, be viewed as limiting the scope of the invention. Theclaims will serve to define the invention.

EXAMPLES Example 1 Control Experiment

The polymerization reactor included a one-gallon, stainless-steelcylinder equipped with a mechanical agitator (shaft and blades) capableof mixing high viscosity polymer cement. The top of the reactor wasconnected to a reflux condenser system for conveying, condensing, andrecycling the 1,3-butadiene vapor developed inside the reactorthroughout the duration of the polymerization. The reactor was alsoequipped with a cooling jacket containing a stream of cold water. Theheat of polymerization was dissipated partly by internal cooling throughthe use of the reflux condenser system and partly by external coolingthrough heat transfer to the cooling jacket.

The reactor was thoroughly purged with a stream of dry nitrogen, whichwas then replaced with 1,3-butadiene vapor by charging 100 g of dry1,3-butadiene monomer to the reactor, heating the reactor to 65° C., andthen venting the 1,3-butadiene vapor from the top of the refluxcondenser system until no liquid 1,3-butadiene remained in the reactor.Cooling water was applied to the reflux condenser and the reactorjacket, and 1302 g of 1,3-butadiene monomer was charged into thereactor. After the monomer was thermostated at 32° C., 29.1 mL of 0.68 Mtriisobutylaluminum (TIBA) in hexane was charged into the reactorfollowed by the addition of 4.6 mL of 0.054 M neodymium (III) versatate(NdV₃). After the mixture inside the reactor was allowed to age for 5minutes, the polymerization was started by charging 5.0 mL of 0.074 Methylaluminum dichloride (EADC) in hexane into the reactor. After 27.9minutes from its commencement, the polymerization mixture was quenchedby diluting with 1360 g of hexane containing 4.6 mL of isopropanol andthen dropping the batch to 3 gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. The coagulated polymer was drum-driedand its characterization is shown in Table 1.

Example 2

The polymerization experiment described in Example 1 was repeated exceptthat 5.0 mL of 0.05 M dicyclopentadiene in hexane was added to the1,3-butadiene monomer before the addition of the catalyst components.Characterization data for the coagulated polymer is shown in Table 1.

TABLE 1 Example 1 2 dicyclopentadiene/Nd 0/1 1/1 molar ratio %conversion 9.5 10.4 ML₁₊₄ 21.3 23.2 Mn (×10³ g/mol) 95 99 Mw (×10³g/mol) 332 334 MWD 3.5 3.4 % cis 98.8 98.9 % trans 0.8 0.8 % vinyl 0.40.3

A comparison of the results obtained in Examples 1 and 2 indicates thatdicyclopentadiene does not inhibit polymerization under normal operationtemperatures.

Example 3 Control Experiment

To conduct this experiment, a Vent Sizing Package (VSP) calorimeter,purchased from Fauske and Associates, was used to perform the runawaypolymerization. The VSP unit, which houses a cylindrical,stainless-steel test cell of 116 millimeter volume, equipped with amagnetic stir bar functioned as the polymerization reactor. The top ofthe test cell was connected to a pressure sensor and thermocouple tomonitor the increase in pressure and temperature. The test cell wascontained in a high pressure bomb under adiabatic conditions. It waspurged with nitrogen and charged with 37.6 g of 1,3-butadiene monomerand 1.4 mL of hexane. The 1,3-butadiene monomer was heated to 32° C. Ina glass bottle, 0.16 mL of a 22.0 wt % 1,3-butadiene in hexane solutionwas combined with 0.84 mL of 0.68 M triisobutylaluminum (TIBA) followedby the addition of 0.13 mL of 0.054 M neodymium(III) versatate (NdV₃) inhexane. Formation of the catalyst was completed after the addition of0.14 mL of 0.074 M ethylaluminum dichloride (EADC) in hexane. Thecatalyst solution was charged via a syringe into the test cellcontaining the 1,3-butadiene monomer, and the temperature and pressurewere monitored throughout the polymerization.

Upon the addition of the catalyst, a rapid increase in temperature andpressure occurred as the polymerization proceeded (see FIG. 1). Uponreaching about 250° C., the polymerization was under runaway conditionsand rapidly accelerated until the abrupt increase in pressure caused thetest cell to rupture.

Example 4

The polymerization experiment described in Example 3 was repeated exceptthat 1.4 mL of 0.015 M dicyclopentadiene in hexane was added to the testcell instead of 1.4 mL of hexane. Upon charging the catalyst solutioninto the test cell, the temperature rapidly accelerated past 100° C.before stabilizing at 146° C. as shown in FIG. 2. The temperature andpressure inside the test cell did not increase for the following 2hours. Upon cooling the test cell, polymerization did not reinitiate. Acomparison of the results obtained in Examples 3 and 4 indicates thatthe presence of dicyclopentadiene prevented an abrupt increase intemperature and pressure, thereby avoiding runaway polymerizationConditions.

Although dicyclopentadiene was found to be a successful polymerizationinhibitor under runaway conditions, several other compounds wereinvestigated as possible alternatives. The results are shown in thefollowing examples.

Example 5 (Comparative Example)

In this experiment, butadiene sulfone was investigated. Thepolymerization experiment described in Example 1 was repeated exceptthat 0.029 grams (0.25 mmol) of butadiene sulfone was added to the1,3-butadiene monomer before the addition of the catalyst components.The polymerization reaction did not occur in the presence of butadienesulfone indicating that butadiene sulfone poisoned the catalyst. Sincebutadiene sulfone is not inert under normal operating polymerizationconditions, it is not a useful runaway polymerization inhibitor for thisinvention.

Example 6 (Comparative Example)

In this experiment, chromium hexacarbonyl was investigated. Thepolymerization experiment described in Example 3 was repeated exceptthat 0.0015 grams (0.007 mmol) of chromium hexacarbonyl was added to the1,3-butadiene monomer before the addition of the catalyst components.Upon charging the catalyst solution into the test cell, the temperaturerapidly accelerated past 100° C. as shown in FIG. 3. Upon reaching about250° C., the polymerization was under runaway conditions and rapidlyaccelerated until the abrupt increase in pressure caused the test cellto rupture. Therefore, chromium hexacarbonyl is not a suitable inhibitorfor the runaway bulk polymerization of 1,3-butadiene.

Example 7 (Comparative Example)

In this experiment, glutaric acid was investigated. The polymerizationexperiment described in Example 3 was repeated except that 0.0028 grams(0.021 mmol) of glutaric acid was added to the 1,3-butadiene monomerbefore the addition of the catalyst components. Upon charging thecatalyst solution into the test cell, the temperature rapidlyaccelerated past 100° C. as shown in FIG. 4. Upon reaching about 250°C., the polymerization was under runaway conditions and rapidlyaccelerated until the abrupt increase in pressure caused the test cellto rupture. Therefore, glutaric acid is not a suitable inhibitor for therunaway bulk polymerization of 1,3-butadiene.

Example 8 (Comparative Example)

In this experiment, a mixture of malic acid and calcium carbonate wasinvestigated. The polymerization experiment described in Example 3 wasrepeated except that 0.0028 grams (0.021 mmol) of malic acid and 0.0021grams (0.021 mmol) calcium carbonate were added to the 1,3-butadienemonomer before the addition of the catalyst components. Upon chargingthe catalyst solution into the test cell, the temperature rapidlyaccelerated past 100° C. as shown in FIG. 5. Upon reaching about 250°C., the polymerization was under runaway conditions and rapidlyaccelerated until the abrupt increase in pressure caused the test cellto rupture. Therefore, a mixture of malic acid and calcium carbonate isnot a suitable inhibitor for the runaway bulk polymerization of1,3-butadiene.

Various modifications and alterations that do not depart from the scopeand spirit of this invention will become apparent to those skilled inthe art. This invention is not to be duly limited to the illustrativeembodiments set forth herein.

1. A method for polymerizing conjugated diene monomer into polydienes,the method comprising: polymerizing conjugated diene monomer within aliquid-phase polymerization mixture that includes conjugated dienemonomer, a lanthanide-based coordination catalyst system,dicyclopentadiene or substituted dicyclopentadiene, and optionallyorganic solvent, with the proviso that the organic solvent, if present,is less than about 20% by weight based on the total weight of thepolymerization mixture.
 2. The method of claim 1, where the conjugateddiene comprises 1,3-butadiene, is oprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 2,4-hexadiene or a mixture thereof.
 3. The method ofclaim 1, where the lanthanide-based catalyst system is formed bycombining (a) a lanthanide compound, (b) an alkylating agent, and (c) ahalogen-containing compound.
 4. The method of claim 3, where thelanthanide compound is a neodymium compound.
 5. The method of claim 4,where the amount of lanthanide compound is present in an amount fromabout 0.001 to about 2 mmol per 100 g of conjugated diene monomer. 6.The method of claim 1, where the molar ratio of dicyclopentadiene orsubstituted dicyclopentadiene to lanthanide compound is at least 0.1 :1.7. The method of claim 1, where the molar ratio of dicyclopentadiene orsubstituted dicyclopentadiene to lanthanide compound is at least 0.1:1and less than 5:1.
 8. The method of claim 1, where the polymerizationmixture includes a compound that is selected from the group consistingof dicyclopentadiene, dimethyldicyclopentadiene,diethyldicyclopentadiene, dicyclohexyldicyclopentadiene, anddiphenyldicyclopentadiene.
 9. The method of claim 1, where thepolymerization mixture includes dicyclopentadiene.
 10. The method ofclaim 1, where the polymerization mixture is maintained below about 80°C.
 11. A method for preparing a polydiene, the method comprising thesteps of: (i) introducing conjugated diene monomer, a lanthanide-basedcoordination catalyst system, dicyclopentadiene or substituteddicyclopentadiene, and optionally organic solvent to a reactor to form aliquid-phase polymerization mixture that includes less than 20% byweight of organic solvent based on the total weight of thepolymerization mixture; and (ii) allowing the monomer to polymerize inthe presence of the lanthanide-based catalyst system and thedicyclopentadiene or substituted dicyclopentadiene within theliquid-phase polymerization mixture to form a polydiene.
 12. The methodof claim 11, further comprising the step of maintaining the temperatureof the polymerization mixture below about 80° C.
 13. The method of claim11, where the reactor includes conjugated diene monomer within thegas-phase, and where the temperature of the polymerization mixture ismaintained at a desired temperature by condensing at least a portion ofthe conjugated diene monomer in the gas-phase to the liquid-phase. 14.The method of claim 11, further comprising the step of removing at leasta portion of the monomer and at least a portion of the polydiene fromthe reactor.
 15. The method of claim 11, where the method is continuous,whereby the conjugated diene monomer, the lanthanide-based catalystsystem, dicyclopentadiene or substituted dicyclopentadiene, andoptionally the organic solvent are continuously added to the reactor,and whereby at least a portion of the monomer and at least a portion ofthe polydiene are continuously removed from the reactor.
 16. The methodof claim 1, where said step of introducing includes introducing acompound selected from the group consisting of dicyclopentadiene,dimethyldicyclopentadiene, diethyldicyclopentadiene,dicyclohexyldicyclopentadiene, and diphenyldicyclopentadiene.
 17. Themethod of claim 11, where said step of introducing includes introducingdicyclopentadiene.
 18. A composition comprising: (i) a lanthanide-basedcoordination catalyst system; (ii) conjugated diene monomer; (iii)polydiene; and (iv) dicyclopentadiene or substituted dicyclopentadiene,with the proviso that the composition includes less than about 20% byweight of organic solvent based on the total weight of the composition.19. A method for polymerizing conjugated diene monomer into polydienes,the method comprising: polymerizing a liquid-phase polymerizationmixture that includes (i) conjugated diene monomer, (ii) alanthanide-based catalyst system, (iii) dicyclopentadiene or substituteddicyclopentadiene, and (iv) optionally organic solvent, wherein saidconjugated diene monomer comprises 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl- 1,3-butadiene,2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, 2,4-hexadiene or a mixture thereof; whereinsaid lanthanide-based catalyst system is formed by combining alanthanide compound, (b) an alkylating agent, and (c) ahalogen-containing compound; and wherein said organic solvent, ifpresent, is less than about 20% by weight based on the total weight ofthe polymerization mixture.
 20. The method of claim 9, where the molarratio of dicyclopentadiene or substituted dicyclopentadiene tolanthanide compound is at least 0.1:1 and less than 5:1.
 21. The methodof claim 20, where the dicyclopentadiene or substituteddicyclopentadiene comprises dicyclopentadiene,dimethyldicyclopentadiene, diethyldicyclopentadiene,dicyclohexyldicyclopentadiene, or diphenyldicyclopentadiene.